1. Field of the Invention
The present invention relates to methods that can be used to count numbers in ascending order in a binary counter under conditions of total security, i.e., without its being possible for a fraudulent individual to disturb the counting in a manner that is favourable to a fraudulent action.
2. Description of the Prior Art
Binary counters are used in large numbers in electronic logic systems for a variety of purposes. In certain cases, it is quite important that the value of the number thus memorized in this counter should be capable of being modified solely through the normal working of the device and not through any external event such as, for example, action by a fraudulent individual or an unwanted operation of the system. However, total security is not always necessary, and it is often far more important to prevent the counter from counting backwards when an excessive degree of forward movement by this counter would only bring about limited disadvantages. For example, there is the particular case of counters that memorize external events in a memory card known as a chip card. These external events may be, for example, the consumption of telephone units or the withdrawal of money from an automatic cash dispenser. It is quite clear that if a fraudulent individual can turn the counter back, he will be able to make excessive use of the card whereas if, on the contrary, all that his action does is to make the counter move forward, it will be of no value to him.
For small numbers, it is of course possible to use a system of the type using memories with fuses, a system that is, by its very essence, irreversible. However, if the number to be counted is a fairly big one, this system proves to be both excessively bulky and very costly.